Medical retrieval assemblies such as baskets generally are used to retrieve biological and foreign material from the body including stones. Such baskets may be used through an endoscope or a laparoscope, for example.
In existing medical retrieval baskets, the contour of the baskets generally are round, oval, or pear-shaped, and the baskets are formed by a plurality of legs. Stones or other biological materials are captured in the basket by moving the basket around the material to be retrieved and maneuvering the material into the basket through the space between the basket legs.
After the material is captured in a known basket, it is generally difficult to release the material from the basket if release of the captured material is required or indicated. The technical difficulty in releasing material such as a captured stone is a characteristic of known medical retrieval baskets in general. In some patients with long-standing clinical problems with urinary tract stones, a cicatrix may form in the tract as a result of trauma to its lining. The stenosis created by the cicatrix may not be so narrow so as to interfere with insertion of a retrieval basket while the basket is in a closed position. However, after the basket is expanded to capture the stone that is lodged beyond the stenotic area of the tract, the diameter of the basket containing the captured stone may exceed the diameter of the stenotic region of the urinary tract. Under these circumstances, release of the stone from the basket is a prerequisite for withdrawal of the device from the urinary tract. If the stone can not be released, more invasive, surgical approaches are required to disengage the stone from the basket.
Also, known baskets must be eased beyond the stone or to one side of the stone to permit entry of the stone into the basket. This maneuver can be technically very difficult. The narrow diameter of the tract lumen, compounded by the formation of stretch resistant scar tissue in the tract at the sites of the stone can severely limit the space around which the basket can maneuver. Moreover, the tract lining may become so attenuated at the site of the stone that advancing the basket to one side of the stone may risk rupture of the tract.
When expanded, existing baskets also generally lack dilatative strength. That is, known baskets generally are not resistive to forces countering basket expansion. The lack of dilatative strength in existing baskets is usually the result of flexible basket legs which are helpful in facilitating the entry of a stone into the basket but which decrease dilatative strength. Consequently, existing baskets generally are not effective at dilating the tract.